Revenue Recognition - Impact to Financial Statements (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues:
Product revenue	$ 3,723	$ 6,600	$ 9,886	$ 12,186
Research and development revenue	9,815	3,747	17,694	6,131
Total revenues	13,538	10,347	27,580	18,317
Costs and operating expenses:
Cost of product revenue	2,611	3,790	6,436	6,792
Research and development	7,370	6,348	14,548	12,187
Selling, general and administrative	7,395	6,546	15,141	13,152
Total costs and operating expenses	17,376	16,684	36,125	32,131
Loss from operations	(3,838)	(6,337)	(8,545)	(13,814)
Interest income	174	49	245	68
Other expenses	(82)	(34)	(142)	(12)
Loss before income taxes	(3,746)	(6,322)	(8,442)	(13,758)
Provision (benefit) from income taxes	(11)	(42)	(13)	(18)
Net loss	$ (3,735)	$ (6,280)	$ (8,429)	$ (13,740)
Net loss per share, basic and diluted (usd per shares)	$ (0.07)	$ (0.13)	$ (0.17)	$ (0.31)
Weighted average common stock shares used in computing net income (loss) per share, basic (shares)	52,787	47,232	50,598	44,258
Assets
Accounts Receivable	$ 9,910		$ 9,910		$ 11,800
Contract assets	554		554		0
Other non-current assets	414		414		302
Liabilities
Other accrued liabilities	5,051		5,051		4,362
Deferred revenue	4,460		4,460		12,292
Deferred revenue - non-current	4,994		4,994		1,501
Stockholders' equity:
Accumulated deficit	(328,026)		(328,026)		(315,065)
Balances without adoption of Topic 606 [Member]
Revenues:
Product revenue	3,269		6,916
Research and development revenue	8,667		15,224
Total revenues	11,936		22,140
Costs and operating expenses:
Cost of product revenue	2,542		5,081
Research and development	7,337		14,468
Selling, general and administrative	7,395		15,141
Total costs and operating expenses	17,274		34,690
Loss from operations	(5,338)		(12,550)
Interest income	174		245
Other expenses	(82)		(142)
Loss before income taxes	(5,246)		(12,447)
Provision (benefit) from income taxes	(11)		(13)
Net loss	$ (5,235)		$ (12,434)
Net loss per share, basic and diluted (usd per shares)	$ (0.10)		$ (0.25)
Weighted average common stock shares used in computing net income (loss) per share, basic (shares)	52,787		50,598
Assets
Accounts Receivable	$ 8,774		$ 8,774
Contract assets	0		0
Other non-current assets	255		255
Liabilities
Other accrued liabilities	3,460		3,460
Deferred revenue	7,369		7,369
Deferred revenue - non-current	1,774		1,774
Stockholders' equity:
Accumulated deficit	(327,971)		(327,971)
Accounting Standards Update 2014-09 [Member] | Adjustments [Member]
Revenues:
Product revenue	(454)		(2,970)
Research and development revenue	(1,148)		(2,470)
Total revenues	(1,602)		(5,440)
Costs and operating expenses:
Cost of product revenue	(69)		(1,355)
Research and development	(33)		(80)
Selling, general and administrative	0		0
Total costs and operating expenses	(102)		(1,435)
Loss from operations	(1,500)		(4,005)
Interest income	0		0
Other expenses	0		0
Loss before income taxes	(1,500)		(4,005)
Provision (benefit) from income taxes	0		0
Net loss	$ (1,500)		$ (4,005)
Net loss per share, basic and diluted (usd per shares)	$ (0.03)		$ (0.08)
Assets
Accounts Receivable	$ (1,136)		$ (1,136)
Contract assets	(554)		(554)
Other non-current assets	(159)		(159)
Liabilities
Other accrued liabilities	(1,591)		(1,591)
Deferred revenue	2,909		2,909
Deferred revenue - non-current	(3,220)		(3,220)
Stockholders' equity:
Accumulated deficit	$ 55		$ 55		$ (4,100)